<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="https://cdn.jsdelivr.net/npm/vue"></script>
    <style>
        .mi {
            width: 300px;
            height: 300px;
            background-color: cornflowerblue;
        }
        .circle{
            border-radius: 50%;
        }
    </style>
</head>
<body>
<div id="app">

    <div v-bind:class='miBox'>
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    </div>

</div>

<script>
    var v = new Vue({
        el: '#app',
        data: {
        },
        computed:{
            miBox:function (el) {
                return {
                    mi:true,
                    circle:true
                }
            }
        }

    })


</script>

</body>
</html>